Interesting post about Maya 2022 (2023 and higher version) and Deformer Sets:
https://forums.autodesk.com/t5/maya-animation-and-rigging/maya-2022-and-deformer-sets/td-p/10599169
Basically they were replaced by Component Tags, which means copyDeformerWeights command cannot normally work to copy weights.
But apparently there is a workaround:
Deformer sets are still supported (and I'm guessing they'll never actually go away for compatibility reasons). You can switch back to them by disabling "Settings > Animation > Use component tags for deformation component subsets". You can turn it back on when it's convenient to migrate over, and existing scenes should work regardless of what that's set to.
